Ceramic fibers have received increasing attention because of new industrial demands for fibers capable of withstanding elevated temperatures without deleterious effects. The growing aerospace industry provides many applications for light and strong heat-resistant fibrous materials. Inorganic refractory fibers commonly available today in commercial quantities include graphite, alumina-silica, boron nitride and silicon carbide.
The formation of inorganic refractory fibers has required elaborate and time consuming procedures since such compounds possess high melting points which render melt spinning either impossible or extremely difficult. Procedures for the thermal formation of fibrous graphite have been proposed in which continuous cellulosic fibers or woven textile articles formed therefrom serve as the starting material. Also, generally infusible synthetic polymeric fibers, such as those formed from acrylonitrile or copolymers thereof, have served as starting materials in processes proposed for the production of fibrous graphite.
U.S. Pat. Nos. 3,270,109 and 3,271,173 disclose processes for the production of inorganic oxide monofilaments in which a precursor fiber composed of certain organometallic salts is formed and then heated to convert the same to the desired inorganic filament. Additionally, inorganic fibers such as those formed from boron or boron carbide have been prepared by the vapor deposition of the same upon a substrate, such as fine tungsten wire.
Other U.S. patents which specifically relate to production of ceramic fibers include U.S. Pat. Nos. 3,107,152; 3,116,975; 3,179,605; 3,270,109; 3,271,173; 3,285,696; 3,311,689; 3,385,915; 3,529,044; 3,760,049; 4,008,299; and 4,126,652.
Ceramic fibers also are finding new applications in the growing electronics industry. There is interest in ceramic fibers which exhibit magnetic anisotropy and high electrical resistivity.
U.S. Pat. No. 2,968,622 describes a process for the preparation of magnetic ceramic fibers which involves attenuation of a molten magnetic material into a fine filament having a mechanically oriented atomic distribution, and followed by rapid chilling thereof to freeze the oriented atomic distribution.
Magnetic ceramic fibers have a wide range of adaptability for prospective applications such as the production of transformers, inductors, switching elements, memory devices, recording heads, tapes, electromagnetic interaction shields, and the like.
Illustrative of prior art of more specific interest in connection with the present invention is U.S. Pat. No. 3,003,223 which describes the production of a textile filament which comprises a metal core and an adherent oriented sheath of synthetic linear polymer.
U.S. Pat. No. 3,075,242 describes a spinneret for the production of hollow polymeric fibers.
U.S. patents which relate to hollow core fibers or composites comprising a polymeric sheath and a core filling usually containing inorganic material include U.S. Pat. Nos. 2,566,441; 3,458,615; 3,500,498; 3,568,249; 3,613,170; 3,875,008; 4,222,977; 4,375,779; and references cited therein.
There remains a need for new and improved processes for the production of inorganic fibers. There is further need for novel magnetic ceramic fibers which can meet specifications for applications such as electromagnetic interaction shielding.
Accordingly, it is an object of this invention to provide an improved process for the production of inorganic fibers.
It is another object of this invention to provide a process for the production of ferrimagnetic spinel fibers.
It is a further object of this invention to provide novel composite fibers comprising a polymeric sheath and a high density ceramic powder core.